The aim of this proposal is to study the regulation of expression and the isolation of muscle protein genes expressed during myogenesis in Drosophila. The biosynthesis of the multiple Drosophila actins will be studied by cell-free translation of actin mRNA and chemical analysis in order to determine their interrelatedness. Translational control of gene expression during myogenesis will be studied by determining the mechanism of translational suppression of actin I mRNA in unfused myogenic cells and by studying the uncoupled transcription-translation of mRNA in EGTA fusion blocked cultures. These studies will involve cell fractionation and mRNA isolation. Transcriptional control of gene expression will be studied by kinetic analysis of homologous and heterologous mRNA and cDNA hybridization reactions. RNA and cDNA will be prepared from cells at different stages of differentiation. These experiments will also be used in the isolation of the structural genes coding for those proteins synthesized as a result of cell fusion. cDNA, complementary to mRNA from differentiated myogenic cells, will be exhaustively hybridized to mRNA from unfused cells. The unhybridized cDNA will be used as a probe to screen established collections of Drosophila genomic recombinant DNA clones. The protein coding sequences of these DNA fragments will be determined by hybrid arrested translation. This DNA will be used to study the organization and expression of the structural genes involved in myogenesis.